The present invention relates to an apparatus for controlling the valves of a four-cycle internal combustion engine. More specifically, the invention relates to a valve control apparatus which renders certain valves inoperative in accordance with the operating conditions of the engine.
In a high-speed four-cycle internal combustion engine, the valve overlap time, that is, the time during which both of the intake and exhaust valves in a cylinder are open is prolonged so that the inertial effect of intake and exhaust gases is utilized to increase the output of the engine. The inertial effect of intake and exhaust gases is useful when the engine is operating at a high speed, but when operating at a low speed, an accompanying reduction in the quantity of the fuel-air mixture introducted into the engine makes the speed thereof insufficient and gives rise to the excess recirculation of exhaust gas. These factors have an adverse effect on combustion, and tend to lower the output of the engine.
There has, therefore, been proposed an engine having a plurality of intake and exhaust valves for each cylinder. When the engine is operating at a low speed, predetermined ones of the intake and exhaust valves are rendered inoperative to increase the flow speed of the fuel-air mixture to thus improve the inertial effect of intake gases and restrict the recirculation of exhaust gas. This engine, however, does not achieve a satisfactory improvement in output during its operation at a medium speed.
In view of these difficulties, it is an object of the invention to provide an internal combustion engine having a maximum output at all engine speeds.